Collaboration is a ubiquitous term that has been defined in numerous ways across diverse fields. This paper draws on information from these diverse fields to begin to develop a theory of collaboration within library science for teachers and library media specialists. In order to fully understand the meaning of collaboration and the relationship between collaboration and student academic achievement, an explanatory theory is needed. Toward the development of such a theory, a definition of collaboration for teachers and library media specialists is proposed. It defines collaboration as a process in which two or more individuals work together to integrate information in order to enhance student learning. The author argues that various notions of working together have been confused with collaboration and proposes four models to distinguish collaboration from other joint efforts such as coordination and cooperation. The models evolve from the literature and from the taxonomy for library media specialists and teachers developed by Loertscher (1982, 1988, 2000). The models are descriptive of the range of joint efforts involved in working relationships that can lead to fully developed collaboration. Numerous attributes--such as collegiality, respect, and trust--needed for collaboration to be effective are discussed. These attributes contribute collaborative activities, such as shared thinking, shared planning, and shared creation of integrated instruction. Two enablers and inhibitors, time and administrative support, are identified from the literature and discussed in relation to collaboration. (Contains 7 figures.)